1. Technical Field
This embodiment relates to a pneumatic tire.
2. Related Art
With respect to a pneumatic tire, there has been known a pneumatic tire where a tread portion includes blocks formed by main grooves extending in a tire circumferential direction and lateral grooves extending in a tire width direction. Particularly in a tire having a large main groove width such as a light-track-use tire, contact patch compression is liable to occur. In addition to such a drawback, in the tire having such blocks, the displacement (movement) of a corner portion of the block is large. Accordingly, the block falls down in a width direction and a circumferential direction of the block, and this falling becomes a factor of causing uneven wear. Particularly, when a plurality of sipes which extend in a tire width direction are formed in the block for increasing a traction performance in all seasons, lowering of rigidity of a corner portion of the block is large and hence, uneven wear is liable to occur.
To suppress contact patch compression by increasing rigidity of a main groove portion, JP-A-2003-154812 discloses a technique where a reinforcing projection projecting in a main groove is formed on a side wall of a block which faces the main groove over a range from the side wall to a groove bottom. This publication also discloses a technique where a plurality of sipes extending in a tire width direction are formed on the block. However, when the reinforcing projection is simply formed on the side wall of the block, particularly in the tire where the block is divided into a plurality of sections by the sipes, the movement of the section positioned at the corner portion of the block cannot be sufficiently suppressed.
On the other hand, JP-A-2002-046422 discloses a technique where, to suppress the reduction of a ground contact area during run flat traveling, a platform is formed in a main groove which defines a block, and the platform is formed of a pair of projecting portions which opposedly faces each other with a gap of a fixed width therebetween. However, the pair of projecting portions is provided for suppressing concave curved deformation of a tread portion by being brought into contact with each other by collapse of a gap therebetween during run flat traveling. Accordingly, this publication discloses neither a technique of projecting a reinforcing projection from side walls of both end portions of a block in a tire circumferential direction nor a technique of connecting the reinforcing projections by a rib extending in the tire circumferential direction.
JP-A-2011-240784 discloses a technique where, to suppress deformation of a main groove, a projecting portion and a cut portion which opens on a groove wall surface are alternately formed on at least one groove wall surface of the main groove along a tire circumferential direction. However, the projecting portion does not extend to a groove bottom and hence, an effect of suppressing falling of a land portion is insufficient.